The present invention relates to the decoding of digital information.
Frequently in dealing with digital information, the incoming information will be in a particular format, whereas it becomes necessary to convert the format of the data into a form that is suitable for subsequent use. In some cases there may be certain restrictions on the nature of the input data format. If the input data is segmented into a plurality of multibit binary words, then the number of different combinations within any given binary word is a function of the number of bits within the word. If a word contains eight bits, for example, 256 different combinations of these "ones" and "zeros" are available. However, if a restriction is imposed on the particular set of "ones" and "zeros", then one no longer has the total 256 combinations available for use. In such case the corresponding decimal numbers that are available would be distributed in somewhat random fashion between the values 0 and 255. It may be desirable, however, that each of the available combinations be utilized to address a particular number within a sequence of contiguous numbers. Consequently, it becomes necessary to decode the input data so as to convert it to the addresses available within the address space of contiguous numbers.
One method of doing this is to utilize a single level table look up method. In this case the table, which is typically stored in semiconductor memory, has a number of locations equal to the number of combinations that are possible in the input code. In the example discussed above, this would be 256. At each location there is an output entry which comprises the decoded address corresponding to the specific input word. The number of memory locations required by this method in some cases is objectionable.